1. Field of the Invention
The present invention relates generally to handwriting data entry, and more particularly to methods and systems for facilitating data entry using a pen input device.
2. Description of the Related Art
Digital writing instruments, interchangeably referred to herein as xe2x80x9cdigital pensxe2x80x9d regardless of whether they write in ink, can be used to capture pen strokes on paper and digitize them, so that the pen strokes can be converted by handwriting recognition software to a digitally-stored record of the writing. In this way, a laborious, tedious step in modern written communication, namely, the manual transcribing of handwriting into a computerized word processor, is eliminated, greatly increasing productivity.
Accordingly, digital pen systems can digitize pen strokes across a substrate, by sensing, in some fashion, the time-dependent position of the pen and converting the positions to pen strokes, for input of digital representations of the pen strokes to a handwriting recognition device. As recognized herein, ultrasonic (xe2x80x9cUSxe2x80x9d) systems can be used in which a special pen generates or alters an ultrasonic signal as the pen is moved across a piece of paper. The US signal is sensed by receivers, correlated to a position vis-a-vis each receiver, and the outputs of the receivers then triangulated and correlated to absolute pen positions. A sequence of pen positions can then be digitized for input into handwriting recognition engines. An advantage with US systems is that the writer can write on an ordinary piece of paper that is placed on or nearby a base station which receives the US signals and converts the signals to alpha-numeric characters.
In US handwriting input systems, a US generator in the pen is energized by high voltage, causing a frame of one or more US pulses to be transmitted. Because of the physics underlying US generation, a single frame consists of not one but many pulses, each being delayed from the immediately preceding pulse by the period xcfx84 defined by the US frequency (essentially, the wavelength xcex of the US signal divided by the speed xe2x80x9ccxe2x80x9d of sound in the medium through which the signal propagates). Of interest is the first pulse, which represents the xe2x80x9ctruexe2x80x9d position of the pen.
One US handwriting device is disclosed in U.S. Pat. No. 5,637,839. The ""839 invention simply uses the first pulse that is detected in a frame as indicating the position of the pen. To alleviate jitter, the ""839 invention averages the positions of several temporally sequential frames.
The present invention recognizes several drawbacks to the above-mentioned prior art US device. First, the first pulse detected might not be the first pulse of the frame, because owing to the physics of exciting a US transmitter with high mechanical Q, the amplitude of the pulses decay after excitation energy is removed. Similarly, the amplitudes of the received signal pulses decay over time. Consequently, if the time of arrival of the first pulse that is detected is used in the computation of pen position, the computed pen position can be an entire wavelength away from the actual position. At the high frame repetition rates (and, hence, very short time periods between frames) that are used to optimize pen position resolution (60-300 frames per second), a positional error of an entire wavelength represents a significant error.
Moreover, the present invention understands that alleviating jitter caused by noise and air currents by averaging several frame positions together slows down the effective frame repetition rate and, hence, reduces resolution. Furthermore, the present invention recognizes that using the time of arrival of the leading edge of a detected pulse can introduce errors, since the pulse width and, hence, temporal position of the leading edge, varies with pulse amplitude. The present invention has considered the above problems and has provided the below-disclosed solutions to one or more of them.
A digital pen system includes an elongated pen defining a writing tip, and an ultrasonic (US) transducer oriented on the pen to direct frames of US energy outwardly from the pen, with each frame including plural receive pulses. At least two detectors are positioned on a base, such as a laptop computer, for receiving the pulses, with each pulse being associated with at least one pulse time of arrival (TOA) relative to at least one detector. A processor is on the base, and the processor receives signals from the detectors and in response thereto outputs position signals representative of positions of the pen based on at least one frame TOA. In accordance with the present invention, the processor determines the frame TOA based on determining that a TOA of a first pulse in a frame deviates from an expected TOA more than a predetermined time period, and/or averaging together plural receive pulse TOAs associated with receive pulses in a single frame.
In a preferred embodiment, the US energy defines a US period xcfx84, and the predetermined time period is one-half the US period xcfx84. The processor modifies either the expected TOA or the TOA of the first pulse by a modulo of the US period xcfx84 when the predetermined time period is exceeded.
As set forth in detail below, the processor stores plural frame TOAs, and the processor modifies stored frame TOAs when the TOA of the first pulse is earlier than the expected TOA by at least the predetermined time period. Further, the processor adjusts the pulse TOAs to the first pulse TOA by subtracting from each ith pulse TOA a period equal to (ixe2x88x921)xcfx84 to render respective adjusted pulse TOAs which are then averaged together to establish the frame TOA.
In a preferred embodiment a pen electromagnetic (EM) device such as an IR transmitter is on the pen, and an EM device such as an IR receiver is on the base for receiving an EM synchronizing signal from the pen EM device. Per present principles, the US energy is synchronized with the synchronizing signal.
In another embodiment, the base EM device transmits the synchronizing signal to the pen. If desired, a contact sensor can be provided on the pen for generating a contact signal representative of the tip contacting a surface, with the pen generating frames based at least in part on the contact signal. In one preferred embodiment, the contact signal varies in proportion to a pressure on the tip, and the pulse width of the signal generated by the pen EM device is proportional to the contact signal.
Also, a grip sensor can be provided on the pen and a high voltage source can also be provided on the pen for energizing the US transducer. The grip sensor generates an enabling signal for the high voltage source.
The preferred processor determines whether the expected TOA is within a lull period (quiet temporal zone), and the processor adjusts a frame repetition rate based at least partially thereon. At least one pulse can be characterized by a leading edge, a center, and a trailing edge, and the pulse TOA associated therewith is a TOA of the center of the pulse.
In another aspect, in a base associated with an ultrasonic (US) pen, a processor includes logic for undertaking method acts that include receiving frames of US pulses from the pen. For each frame, a measured time of arrival (TOA) of at least one pulse is modified based on at least one US period to generate a frame TOA.
In still another aspect, a logic device is disclosed for executing method acts for electronically associating sensed handwriting on an actual form with fields of an electronically-stored virtual form. The method acts executed by the logic device include sensing at least one form location of the actual form relative to a base. The form location has a corresponding virtual form location in electronic memory. Handwriting on the actual form is sensed, with the handwriting having a handwriting location relative to the base and with the handwriting location being digitized into a corresponding virtual handwriting location in memory. The method undertaken by the logic device also includes associating the virtual handwriting location with the virtual form location.